The invention relates to an apparatus for synchronizing an electronic flash with a camera including a focal plane shutter for the purpose of taking a picture under flashlight. When an electronic flash is used to take a picture under flashlight with a camera including a focal plane shutter, the synchronizing contact must be changed to the X contact. Simultaneously, the exposure period must be previously controlled so that a shutter speed or exposure period assumes a value at which a synchronized flashlight photographing is possible (which is referred to hereinafter as X-period), which is usually set to be greater than 1/125 to 1/60 second. Such value of the shutter speed corresponds to an exposure period which is defined from the termination of movement of the first blind of the shutter to fully open an exposure light path until the second blind moves to close the open exposure path. Such pre-establishing of the shutter speed is necessary because a focal plane shutter employs a slitwise exposure while an electronic flash represents a source of flashlight having a very short duration. If a picture is taken with a shutter speed established on the order of 1/250 second or the like, only one-half or one quarter of the scene to be photographed will be irradiated by the flashlight. This explains why the shutter speed must be established to an X-period. However, it often occurs that a photographer forgets to set the shutter speed to correspond to an X-period when taking a picture under flashlight, and becomes aware of this fact only after the exposed film is developed.
When using an electronic flash to take a picture under synchronized flashlight, it is known that the intensity of reflected light from an object being photographed varies as the distance between the camera and the object varies, thereby necessitating an adjustment of the diaphragm each time a picture is taken. To avoid such inconveniences, an adjusted flashlight emitter referred to as auto-strobo has been recently developed. This comprises a flash tube bypassed by a discharge tube in combination with a photometric circuit which is operative, upon illumination of the flash tube, to measure reflected light from an object being photographed and to cause a discharge of the discharge tube when the amount of light being measured reaches a proper amount of exposure, thus short-circuiting the flash tube to interrupt its operation and thus assuring a proper exposure. As is well known, an EE camera includes its own photometric circuit, which however is not used when the above mentioned auto-strobe is used to take a picture under flashlight.
Another difficulty occurs with the combination of the auto-strobo and an EE camera having an electronic focal plane shutter. The illumination of the strobe is controlled by the X contact which is closed by the operation of the shutter within the EE camera, which is in turn controlled by the EE circuit. Specifically, a release operation of the shutter causes the first blind of the shutter to move, and the X contact is closed when the photographic path becomes open. As the reflected light from an object being photographed reaches a proper amount of exposure, an electromagnet which has been constraining the second blind of the shutter from moving is deenergized to permit movement of the second blind, thus terminating a photographing operation. The arrangement is such that if a given amount of exposure has been reached by natural light before the X contact is closed, an inhibit signal is applied to the strobo unit. However, depending on the relative timing of the inhibit signal generated and the closure of the X contact, the X contact may be closed to cause an illumination of the strobo unit. At this time, since the second blind of the shutter has already moved into the photographic path, vignetting is caused on the film surface by the presence of the second blind, thus resulting in a failure of synchronization.